Submarine cable



Dec. 20, 1932.

SUBMARINE CABLE Filed Feb. 12, 1931 FIG. IB

FIGIA E. K. SANDEMAN ET AL 5 Sheets-Sheet 1.

ll It INVENTORS EDWARD K. SANDEMAN PHILIP R. THOMAS SYDNEY H. GROVE zw M ATTORNEY Dec. 20, 1932. SANDEMAN vET AL 1,891,244

SUBMARINE CABLE Filed Feb. 12, 1931 5 Sheets-Sheet 2 FIGI C INVENTORS EDWARD K. SANDEMAN 3 PHILIP R. THOMAS u SYDNEY H. GROVE ATTORNEY 1932- E.'K. SANDEMAB! ET AL. 1,391,244

SUBMARINE CABLE Filed Feb. 12,-1951 5 Sheets-Sheet 5 9 v 9 L1. m LL L INVENTORS S EDWARD K. SANDEMAN m PHILIP R THOMAS SYDNEY H. GROVE ATTORNEY 1932- E. K. SANDEMAN ET AL 1,891,244

SUBMARINE CABLE Filed Feb. 12. 1931 5 Sheets-Sheet 4 ATTORN EY Dec. 20, 1932.

FIG. 4A

FIG. 4.

E. K. SANDEMAN ET AL SUBMARINE CABLE Filed Feb. 12, 1931 5 Sheets-Sheet 5 INVENTOfiS EDWARD K. SA DEMAN PHILIP R..THOMAS SYDNEY H. GROVE ATTORN EY Patented Dec. 20, 1932 marten stares PATENT orrics EDWARD K. SANDEMAN, PHILIP R. THOMAS, AND SYDNEY H. GROVE, OF ALDWYCH, LONDON, ENGLAND, ASSIGNOBS TO INTERNATIONAL STANDARD ELECTRIC COR- PORATION, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE SUBMABINE CABLE Application filed February '12, 1931, Serial No. 515,256, and in Spain Apri1 29, 1930.

\ sion, delay networks well as telephony and This invention relates to submarine cable telephone transmission systems. In such systems wherein it is required to transmit telephone signals between two stations separated by long distances, it is necessary to have means at the terminals of the cable for directing to the proper amplifiers the telephone signals according to their direction of transmission.

It has heretofore been proposed to accomplish this by using a balanced transformer for coupling the transmitting and receiving branches to the cable terminal. This arrangement had many disadvantages mainly due to the impossibility of obtaining or maintaining accurate balance, which gives rise to interference between the two branches.

The present invention provides an improved system and broadly comprises a submarine telephone cable transmission system comprising terminal amplifiers and means controlled by voice frequency currents for operating the switching of the terminal amplifiers according to the direction of transmisfor preventing undue loss of signals during the switching operations in combination with means which in known manner momentarily protect the receiving apparatus from discharge currents immediately after the terminal connections are switched from the transmitting condition to the receiving condition.

Furthermore the invention as above may be represented in different practical embodiments or alternatives which will be described hereinafter so that the full scope of the invention may be readily understood.

Other features also contributing to the practical success of the invention will also be I evident from a perusal of the following description and will be pointed out more clearly in the appended claims. I

It may sometimes be desirable that the cable system provides the following description will reveal how the telephone system according to the invention may by a modification be used in a system over which both telephone and telegraph communications may take place. The direction of telegraph transtelegraph facilities as.

mission may be either dependent or independent of the direction of speech.

In the accompanying drawings Fig. 1 illustrates the invention as applied to the terminal equipment for a system adapted solely for telephony.

Fig. 1A illustrates a suitable means for connecting the equipment of Fig. 1 to a land line.

Flg. 1]?) illustrates an arrangement whereby the switching controlled according to the arrangements of Fig. 1 may be extended over a repeater situated at an intermediate point in the cable circuit. 1BFig. 1C illustrates a modification of Fig.

Fig. 1D illustrates an arrangement which when connected to either points A and A or B and B of Fig. 16 will terminate the cables CV and CE respectively so that the equipment of Fig. 1C may serve either as a repeater over the extreme ends of the cable or as a terminal for either cable which is connected to it.

Fig. 2 is a schematic diagram illustrating a cable provided with telegraph facilities as well as telephony.

Fig. 3 shows a modified arrangement according to the invention also for telephone and telegraph and in which courier currents are used for switching.

Fig. 3A illustrates a repeater arrangement using courier current control.

Fig. i and Fig. 4A illustrate terminal equlpment of a submarine cable telephone and telegraph system.

WVith reference to Fig. 1 the arrangement will be best understood by reference to the functioning of its parts. Suppose that telephone signals arrive on line L on the top left hand of the figure, they are passed through amplifier A5 and reach a branching point. The main signals pass to a delay network D2 where the transmission of the messagein this direction is delayed for a predetermined period. Meantime the currents traversing the other branch path traverses an amplifier detector (preferably made sensitive only to that part of the frequency range which lies below about 1,200 cycles per second) AD in whose output circuit is a winding for operating relay S This relay on operation closes a circuit for relay S and removes a short circuit from the relay of switch LS The function of the relay S; will be explained later.

Switch LS closes its inner contacts and thereby connects the line L to a transformer T lVhen this has taken place the speech signals have traversed the delay network D2, an equalizer E which is adapted partially to equalize the attenuation of the signal frequencies to be transmitted over the cable, and the amplifier A to the switch contacts LS AVCl is an automatic volume control device for controlling the output from the amplifier A V1 is a volume indicator for measuring the actual level of the speech being delivered to the submarine cable. VL is a voltage limiter which will be explained later.

During the transmission of speech from line L to the transformer T1 (which may be iron or air cored) the circuit of line L is short circuited by the switch S lVhen the speech input from the line L ceases, relay S releases. S however does not release until later than LS after the cessation of speech, thus ensuring that any noise occurring at the moment of connectlon of the receiving branch L to the transformer T Wlll not be transmitted through the line L. lVhen the speech is received over cable C it passes through transformers T and T over the switch LS outer contacts to an amplifier A10. It then traverses an equalizer E which is designed to complete the equalization of the signals transmitted in this direction which were partly equalized at the transmitting end. The signal then traverses an amplifier A amplifier A to the line L V1,. is a volume indicator similar to V1 Between the amplifiers A and A a branch path is taken th 'ough an amplifier detector AD for operating the switch S which when energized short circuits the amplifier A and amplifier-detector AD connected to the line L The release of the relay S is delayed for the cessation of speech by a time equal to twice the transmission time of the four-wire circuit L L this prevents the false operation of amplifier detector AD and the relays S S and S by echo currents from the termination of the circuit.

In the above description we have referred to speech signals arriving on line L and being received in the line L In Fig. 1A there is shown an arrangement for connecting the lines L and L to a land line such as TB Signals arrive in line TB from a subscribers station; they pass through the balanced transformer HCl of ordinary construction employing a balancing network N. They then pass through amplifier Al in whose input circuit is a gain control device GCl which is either under the control of the voice currents or may be manually controlled. In

the output of A1 is a branch circuit leading through a delay network D through an amplifier A and to the line L The other branch is through an amplifier detector AD which controls the switch S which shortcircuits an amplifier in the line L Transmission in the path L from the amplifier A6 of Fig. 1 takes place over amplifier A gain control device G0 amplifier A to the transformer HC The output of the amplifier A is shunted by an amplifier detector AD for operating a switch S which shortcircuits amplifier A1 in the transmitting branch. The relay S is shown having the second winding connected through a rheostat VHO. The object is to vary the release time of the relay S after the cessation of the speech from the line L This is delayed so that the relay S will not be released until all echoes received from extensions connected to TBl have been received and suppressed by the contacts shortcircuiting the input to the amplifier detector AD In Fig. 1B a telephone repeater equipment is illustrated such as may be situated in an island lying intermediately in the cable route. The equipment uses branches for conducting the signal from either direction through a power amplifier A12. The repeater is normally conditioned for through transmission in neither direction but is so adapted that on receiving signals from one direction a through circuit is established whilst the branch adapted to receive in the opposite direction is disabled.

A signal arriving from cable CW to the transformer T T passes over the outer contacts of switch LS over amplifier A equalizer E amplifiers A and A to a delay net work D Across the output of the amplifier A is shunted an amplifier detector AD for operating a relay S This relay in turn operates relay S, which on closing its contacts shortcircuits an amplifier A in the branch adapted for transmitting in the opposite direction and this branch is therefore disabled. The switch S in operating also removes the shortcircuit from the switch LS which closes its inner contacts. These switching operations are adapted to take place during the delay in the signals by the network D From this network the sig nals pass through the power amplifier A and to the inner contacts of switch LS and thence through transformers T and T to the cable CE. VL in the output of the amplifier 12 is an equipment for adjusting signal levers. Signals received in the opposite direction, i. e. from cable CE pass through the outer contacts of switch LS through amplifier A equalizers E. amplifiers A and A to the delay network D power amplifier A and to the inner contacts of switch L53 to the line, the contacts of switch LS being closed by means of switch S over the amplifier dere -inn tector AD which operates similarly to the equipment already described for the opposite direction of transmission. Similarly S shortcircuits the amplifier A The sh0rtcircuit placed on amplifiers A or A respectively by the relays S and S1 Protects the amplifier A from noise from the unused branch during the transmission of speech.

In Fig. 1C is illustrated a modification of a repeater equipment which might substitute that of Fig. 3. This equipment, however, provides the additional facility that it may be used either as a repeater from the cable CW to the cable CE or it may be used as a terminal equipment for both the cable CIV and the cable CE. We shall describe later the additional apparatus which may be adapted to the equipment of Fig. 1G to enable this additional facility to be used. The equipment of Fig- 1C is practically identical with that of Fig. 113 with the exception that no common power amplifier is used, but instead two separate amplifiers A and A are provided. The switching conditions and the shortcircuiting relays are indicated by similar reference letters as in Fig; 1B and since the operation is substantially the same it is thought that its operation will be evident without detailed description.

In Fig. 1D an equipment is shown which may be connected to the circuit of Fig. 10 so that the terminals A correspond with the terminals A or B and the terminals B corre spond respectively to the terminals A or B In the first case it would act as a terminal equipment to the cable CW and in the second case it would act as a terminal equipment to the cable CE. Assuming the contacts of A correspond to B and B to B the amplifier A would be connected to a delay network D and the delay network D to the amplifier A Signals received from the cable CE would pass through amplifier A through delay network D gain control de vice GC amplifier A to the hybrid coil HC and the land line SE I Vhen transmitting in the opposite direction, signals from SB pass over the transformer I-IC through the gain control device G0 amplifier A tothe delay network I) of Fig. 1C. The function of the gain control devices and the delay networks with the switch gear of Fig. 1C is as before explained.

In the above arrangements there are no facilities provided for telegraph transmission, but this may be converted into a system for transmitting telegraphy as well as telephony by following the arrangements shown schematically in Fig. 2. In this figure the telephone branch from the cable C is over a filter TP which is adapted to pass telephone frequencies but to offer high attenuation to telegraph frequencies. Switch LS corresponds to the switch of Fig. 1 bearing the same reference and the branches L and L also correspond with branches L and L of Fig. 1. The repeaters and other apparatus in these respective branches are indicated schematically by R and R The two branches L1 and L terminate as before in the line T13 The telegraph equipment for transmitting and receiving is connected to the cable C over the switch TS which when on its upper contact connects the telegraph receiving apparatus It through the amplifier R3 to the cable C through a filter TG which is adapted to transmit telegraph currents and to exclude telephone currents. hen the switch TS is on its lower contact the telegraph transmitter- T is connected through the amplifier R and filter T,; to the cable. The switch TS may be arranged to operate directly under the control of the switch LS so that the movement of switch LS causes a similar movement in the switch TS. A means for effecting this may be merely by connecting the two switch arms together as will be obvious. With such an arrangement the telegraph transmission will always be in the same direction as speech and known means would have to be provided for storing the telegraph messages during intervals of interruption due to the voice frequency switching. In a modification the switch TS may be quite independent of the switch LS1 and may be governed in operation by the direction of telegraph transmission which is to take place over the cable, thus the first telegraph transmitter to function may be given control over the line by switching arrangements substantially the same as those employed for telephony in Fig. 1.

In F ig; 3 a system is shown in which the speech currents have not entire direct control of the switching,

In this system both speech and telegraph currents may be transmitted simultaneously, the direction of the telegraph current not being controlled in any way by the direction of the speech currents. The circuit is normally arranged for speech transmission in the direction opposite to that of telegraph transmission. One of the telegraph channels is reserved for the transmission of control currents to operate switchgear in the voice cirl cuit, speech for transmission in the same direction as telegraph starts these control currents which operate the switchgear in the remaining part of the system unless the complete system is occupied by speech in the normally through direction. In this case a courier current is employed for controlling the switching of the telephone receiving and transmitting branches ofthe cable. In the figure the switches are in a position to connect the telegraph receiver to the cable. The terminal equipment of Fig. 3 is somewhat similar to that of Fig. 1 and similar parts in both figures bear the same reference letters. In the transmitting branch L a filter ISO F is provided for preventing telegraph frequencies from entering the cable and a similar filter F 2 is provided in the branch L lVith the switches in the position shown in Fig. 1 the branch L is connected through the transformers T T and a filter F to the cable C. The terminal equipment at the other end of the cable C may be identical with that of Fig. 3 and at that station the switch corresponding to LS would be in a position to connect the cable to the receiving branch corresponding with L. If there is no transmission in the branch L and a person at the other end of the cable begins to speak, a courier current is transmitted along the cable and received through the filter F over the closed contacts of switch TS through equalizer TE, amplifier TA, receiver TR to a relay S which on closing its contact connects earth over the relay S S on operating breaks the energizing circuit of relay S which on releasing ensures that earth is disconnected from the left hand side of the polarized relay S so that the connection of the other side of said relay to earth switches TS and S38 causes the armature of relay S to move to the right breaking the circuit of relay S which de-energizing causes its armature to move to the lower contact for energizing switch LS Before this can take place, however, a momentary contact has been made from earth through the armature of S to relay S which momentarily shortcircuits the transmitting branch L just before the switch LS closes its inner contacts to the line through transformers T T When de-energized relay S32 also breaks the energizing circuit for relay S which prevents earth being put on the winding of relay S by manual operation of the switch TS so that after having established the circuit at the receiving end the speaker at the remote station maintains control of the circuit as long as he continues H to speak.

On the inner contacts switch LS being closed the telephone currents pass through the filter F amplifier A equalizer E2, amplifier i8, amplifier A6 to the line L Some of the current passes through the amplifier detector AD operating relay S which breaks the circuit of the amplifier detector AD so that the control of the relay S from line L is broken. This holds the circuit for reception in L independent of courier as long as the speech is continued. lVhen speech in this direction ceases, however, rela S releases freeing relay S On deenergizing relay S closes its contact. IVith the cessation of speech relay S de-energizes allowing its contact to close. Thus the circuit of S is re-established and on the receipt of speech in L will again place earth on the winding of relay to bring its armature to the left as above explained. Relay S closes courier current C to the line over T3 and filter F4.

In Fig. 3A a repeater similar in function to that of Fig. 1B is shown adapted to repeat in a system employing the courier current control. The same reference letters in Figs. 1B and 3A indicate like parts and their func tions will not be again explained. Assuming telephone transmission be taking place from Cl/V to CE, the switches would be in the position shown. They pass through filter F to the outer contacts of switch LS over the branch comprising filter F etc. to the delay network D amplifier A12, filter F8 to the outer contacts of switch LS and thence through transformers T and T and filter F to the cable CE. All the filters F F F F F are adapted to transmit telephone frequencies and suppress telegraph frequencies.

Suppose that speech in the said direction from (DIV to CE ceases and telephone current is received at CE from the opposite direction, then this speech would be preceded by a courier current which would traverse filter F switch T8 over amplifier TA, equalizer TE, phase compensator PC, zero wander corrector ZVV, courier receiver REG, to relay S which on being operated places earth on the relays LS and LS closing the inner contacts thereof. This would connect the cable CE through filter F amplifier A6 through D A F inner contacts of LS to the cable CIV over the transformers T T The telegraph switches T3 and TS for controlling the telegraph transmission are for simplification shown as manually operated simplex, and the co-operation between attendants to control the direction of transmission is on the well known simplex basis.

When switches T8 and T5 are positioned for telegraph transmission in the opposite direction i. e. from GIV to CE, the switches LS and LS are normally operated and provide a telephone circuit from GE to (WV. In such a case when relay S is operated by the receipt of courier the switches LS and LS are released changing the direction for telephone transmission.

In Fig. 3.5 we have shown how the principle of Fig. 113 may be modified for a system with courier current control and in similar manner the system as illustrated in Fig. 10 may also be adapted with suitable modification for a system with courier controlled switching.

Figures 4: and 4 A show the terminal stations of a submarine cable telephone and telegraph system in which the transmission features are similar to those previously described for other systems. In this system the direction of telegraph transmission is dependent on the direction of telephone transmission and is always in the same direction. The system is normally in a condition for through transmission of both telephone and telegraph currents from the station shown on Figure 4--A to that shown on Figure 4.

Considering the operation of the station shown on Figure 4; speech received for transmission to the submarine cable along the line L causes the amplfier detector AD; to operate the relay S whch short circuits the receiving apparatus, and the amplifier detector AD connected between the submarine cable and the line L The relay S causes operation of the line switch LS for changing the connection of the submarine cable from the receiving apparatus to the transmitting amplifier associated with the line L This relay also causes the operation of the switch TLS which performs a similar function for the telegraph circuit. The operation of the switch S causes the operation of the switches S and S which are so timed that the switch S operates before S thus sending a pulse of control current from the source of the control current C through filter F to the submarine cable. The cessation of speech on the line L allows the switch S to release the switches S and S and these are so arranged that the switch S releases before the switch S thus sending another pulse of control current to the cable. There is thus a pulse of control current before speech, which is delayed by the delay network, and a second pulse after the cessation of speech.

In the normal condition of the switch LS received telephone currentaenters the apparatus connected to the receiving line L and by means of the amplifier detector All causes operation of theswitch S which short circuits both the input to the amplifier detector AD and part of the apparatus connected to the line L, thus preventing interference from noises and speech on the line L The switch TLS may have an extra contact which can be arranged to start the telegraph transmitter when the switch TLS is in a position for the transmission of telegraph signals through the filter F to the cable. The filters F F and F are designed to discriminate between .the various currents required by the parts of the system connected to them. All the amplifiers in this figure are designated A.

In Figure 4-A the line L, is connected through the transmitting amplifiers A to the contacts of the switch LS to the submarine cable. Extra contacts from this switch are arranged to short circuit the output of the intermediate stage of the receiving amplifier A The telegraph transmitter is also normally connected through the filter F to the over the normally made contacts of the re- I lays S and S to cause operation of the relay S The operation of this relay causes the operation of the line switch LS and the telegraph line switch TlLS which connects both the telephone and the telegraph receiving circuits to the submarine cable and prepares them for the reception of speech and telegraph respectively. After the cessation of this first pulse the relay S remains operated through its contact and the winding of relay S and the normally made contact of relay S The removal of the earth from the winding and contact of the relay S allows the relay S to operate. The operation of the relay S connects the lead from the relay S through the winding of the relay S and battery. speech causes operation of the relay S5. The operation of the relay S disconnects the earth from the windings of relays S and S7 which then release causing the relays LS and TLS to release, thus restoring both telephone and telegraph circuits tothe transmitting condition. I Vhen the relay S releases after the pulse, relay S releases and the train I consisting of the relays S S and S are again ready for the reception of the pulses preceding and following the next period of speech.

The extra contact on the switch LS is ar i graph and 400 to 2,400 cycles for telephony,

the space 300 to 400 cycles being unused to allow for the slope of the separating filters. In the case of dependent telegraphy this space can be made less than in the case of independent telegraphy because the attenuation necessary in the filters is smaller. The method in which the telegraph frequency range is occupied by telegraphy may differ in different cases but the use of a multiplex system oc-' cupying the range 0 to 100 cycles is contemplated while the range 100 to 800 cycles could be occupied by a similar multiplex system operated on carrier frequency of 200 cycles. An alternative method is to use a high speed distributor which may be of the thermionic valve type, transmitting at 600 bands. An alternative method where independent telegraphy is possible and which is'probably preferable since it gives the effect of duplex working,

The reception of the pulse following is to use the range 0-150 cycles for telegraph working in one direction and 150300 cycles for telegraph working in the opposite direction. It will be understood that all figures quoted are merely given as examples and that circumstances might cause them to be considerably modified in value. In the case where full telegraph working is used over the system (i. e. without telephony) the whole frequency range which may be of the order of 0 to 2,400 cycles may be occupied by a number of voice frequency telegraph channels ob tained by the modulation of a number of separate voice frequencies by different transmitting devices. Each transmitting device may be an ordinary telegraph transmitter or a number of ordinary transmitters operating through synchronized multiplex distributors. These distributors may be of the ordinary me chanical rotary type. or may be of the thermionic valve type. Transmission of the signals impressed on any carrier by modulation may be secured by sending both resultant sidebands and the carrier, by sending one sideband and the carrier or by sending one sideband alone. The last mentioned method is evidently preferable because it enables a larger number of channels to be obtained in a given frequency range. Synchronization of the telegraph signals can conveniently be carried out by a frequency located either in the speech range or in the telegraph range or outside or between the two; or alternatively synchronization by means of the signals themselves may be employed. In the case where a synchronizing frequency is employed within the range of speech for telephony, suitable means will be provided to balance it out at the receiving end. In the case where dependent telegraphy is employed and where the direction of telephony is changed from inst-ant to instant with the direction of speech, known means will be employed by which controlled synchronizing oscillators at each terminal alternatively hold in step, and are held in step by each other as the direction of transmission changes.

In some cases it may be desirable to change the location of the speech range in the frequency spectrum by any suitable known process of modulation. For instance a speech range which may extend from 400 to 2,400 cycles per second could be moved to the range 0 to 2,000 cycles per second before transmission over the cable and could be reconverted at the receiving end.

What is claimed is:

1. In a submarine cable telephone system the combination with the cable of a circuit comprising a receiving branch and a transmitting branch, a switching device in said circuit adapted to connect said cable respectively with either the receiving branch or the transmitting branch and means for operating said switching device by voice currents in said circuit.

2. In a submarine cable telephone system the combination with the cable of a circuit comprising a receiving branch and a transmitting branch, a voice current detecting device in each said branch, an amplifying device in each said branch, a switching device in said circuit adapted to connect said cable respectively with either the receiving branch or the transmitting branch under the control of voice currents in said circuit according to the direction of transmission and means under control of said Voice current detecting device in one branch to disable the amplifying device in the other branch and Vice versa.

3. In a submarine cable telephone system the combination with the cable of a circuit comprising a receiving branch and a transmitting branch, a switching device in said circuit normally positioned to connect one branch to said cable and means associated with the other branch and operative by voice currents therein to operate said switching device to connect said other branch to said cable.

4. In a submarine cable telephone system the combination with the cable of a circuit comprising a receiving branch and a transm1tting branch, a switching device in said circuit normally positioned to connect the receiving branch to said cable, means associated with the transmitting branch and operative by voice currents therein to operate said switching device to connect said transmitting branch to said cable and means in said transmitting branch to delay the transmission of voice currents to the cable.

5. In a submarine cable telephone system the combination with the cable of a circuit ed to be operated by voice currents therein to operate said switching device to connect said transmitting branch to said cable and to disable the amplifying means in said re ceiving branch.

6. In a submarine cable telephone system the combination with the cable of a filter adapted to pass telephone frequencies, a filter adapted to pass telegraph frequencies, a telephone circuit comprising a receiving branch and a transmitting branch associated with said first mentioned filter, a telegraph circuit comprising a receiving branch and a transmitting branch associated with said second mentioned filter, switching means adaptated with the transmitting branch and adapted to connect said cable respectively either with said receiving branches or said transmitting branches and means operated by voice frequency currents for controlling said switching means.

7. In a submarine cable telephone system comprising terminating equipment at each end of the cable including transmitting and receiving branches and switching devices for connecting the cable alternately to said branches, the combination with the switching device at one end of the cable of means responsive to control currents transmitted over the cable and adapted to cause the oplv eration of said switching device and means at the other end of said cable responsive to voice currents for controlling the transmission of said control currents.

In witness whereof, we hereunto subscribe :0 our names this 26th day of January, 1931. EDWARD K. SANDEMAN. PHILIP R. THOMAS. SYDNEY H. GROVE. 

